Oil base drilling fluid



. on. BASE DRILLING FLUID a James L. Lummus, Tulsa, 01th., assignor to Pan Ame'nican Petroleum Corporation,; a corporation of Dela- Ware 7 i i v 'No Drawing. Filed An, 1956, Senna-591,618 i "9 Cla'i'ms. n w. a

This invention relates tothe art of suitablefluids'for :drilling, completing and otherwise servicing wells. More particularly it relates to oil base drilling fluids which. are

"stable to water contamination. This isa continuation-inipart of my copending U.S. patent application Serial "tNumber'327,'163,.entitled OiLBaseiDrilling Fluid, filed December 20,1952, now abandoned.

a dispersion of these particles in oil, is ,stableat high The artjof oil base::drilling fluidsisconfrentedwith "a number of problems. A principal problem is the'high acost 'of present commercial oil base drillingfluid. This high cost-is due.prineipally to the expense of treating the soil base with plastering agents to reduce-the fluid-loss, V nd with :bodyingaagents ,tolixnpart .gel strength ,or,

osity suflicient'j to suspend, weighting materials; An-

are generally highly susceptible o shale contamipatibn. That is, if 'theoil base cont-ains watergthis water tendsfto swell" clay contacted by the, drilling" fluid, usually with the result that "viscosity and sometimes gel sti'e'ngths become excessive. -Stillanother problem' faced jby the oil =ba'se drilling fluid art is that of increased fluid lossz at-h igh temperatures. This is'due tothe decreased .elfectiveness of most plastering agents, such as blown asphalt, at

.high temperatures. Gel strengthviszalsoaa vconsiderable 'other ,problem is ,wa t'er contamination which appears to Lil a-unavoidable during drilling operations. ;Thiswater an come either from,forrnati ons; drilled or. fr o1n'sur'tace fjrun olf and thelike f water :cohtaminatedldriliingfluids alternates of these materials.

( duce oil suspensions having low fluid loss. the plastering materials are little affected by tempera- 15 ,ties such as fluid loss and gel strength. Thus, the simple 2,943,051 Patented June 28, 196i) ice In general, I accomplished the objects of my invention by coating finely divided solids with a combination of calcium chloride and lecithin oi, in some cases, certain I have found that calcium chloride and lecithin appear to react to form a product which seems to retain the surface activity of lecithin so that the material tends to concentrate on surfaces of solids exposed to solutions orsuspensions of the material. When the material is deposited on finely divided solids, the

particles disperse readily in oil. Thecoated particles have been found to impart gel-strength to the oil. The

treated solids also have plastering properties which pro- Being solids,

.ture. Therefore, temperature has little'eifect on properand inexpensive coated. particles are capable of performing the gel-forming and fluid loss reducing functions of the many andexpensive additives used in priorcompositions. 1 In addition, the oil base drilling fluid, formed by in nature since hit acts as an efiective emulsifyinggagent are; protected from .water by the composition and are suitable as finely divided solids formy purposes. Y

.=A coating of calcium chloride and lecithin is also'eflfec- -:tive in;pr6tecting.hydi-ophilie solids in many:ofthe presently .availableucommerciall oil base drilling fluids; Such materials are quick'li-mehas .in U.S. 2,356,776, Miller;

lalka'li metal soap's as in U.S.. 2,350,154, Dawsonet and U.S. 2,573,960, Fischerj orsolids treated with sur- 'face active agents as described in co-pending U.S. patent application 144,856, filed February 17, 1950, now abanproblem in oil base drilling fluids. ,Many such iluids have no gel. strength,atzall-"andqthus, .must relay; on

. viscosity alone to carry,bit cuttings fron a well. Qther oil base drilling fluidsis uifer from problems ,at' the other extreme. ,Ihat is," ,they have fexcessivelyghigh lg el f'hydratable shales. If "a drilling" fluidflhas little gel :strength, a principal problem is to suspend weighting materials in this -drilling 'fluid -to increase the density to desired levels.

With the-above -problems and difliculties' inmind, an object of this invention: is to 1 provide an improved. low

acost oil base drillingfluids Another, object .is toiprovide 1 r :an oil base drillingyfluid-which" will :withstand ,water wand shale -.contaminat ion.,. Still| another object is tozgproa a l b ri i g. .flu dww c ,hasavlow uid i "w even ethi h mmemmwa- M a to provide anoil bas fluid .havingla; gel strength I Anothereobject is to provide an oil vbase drilling, fluid in which weighting I "materials are. easily suspended. Aspecificobject isto proyidea coat-r edfinely;divided solidgresistant to water an having ,I. to.,act not only in it's. usuaiaveighting'oapacitybutalso V additionalobject is' within desirable limits.

p steri andg ri rmin jp bper ies hsnjadd ito an base; 'Anothersspecific object is to provide a method l and composition for treating 'finely divided solids suspendedin an oil base to disperse theparticlesjand impartto-t-he particles plastering andjgel-forming propen ties and resistance to water contaminationrdA still more specific j object is {to provide a method and composition for stabilizing -'presentoil basedrilling-fluidsfagainst waj ter contaminationl .7

esltreu'gthjs, particularlyfwhen contaminated witliwateriand 'doned, Thus, when commercial oil'base drilling fluids now available are treated with calcium chloride and :lecithin, the hydrophilic solids are stabilized to watercoutamination amounting to as much as do'percent of the resulting emulsion. When present oil base drilling fluids become contaminated with-water, and' hydratable shale is drilled, the shale particles produced by. the-bitoften iswell and thicken the' d'rilling fluid excessively, The. lecithin-and ealcium chloride apparently coat these shale particlea preventingshalehydration by the water. Thus,

."lecithinibelngi about the same as in present commercrai noilvbase drilling fluids, .even though: none-of the usual acl dit ives for increasing gel strength-and viscosity are pre'sently' available commercial oil base drillingfluids are =ix-also protected against the; adverse efiects of shale contamination by my treatment.

" Ihe treatment is also capable of dispersing-'finelydividedweighting materials, the settling r'ate of particles of weighting materials coated with calcium chloride and employed with the coated particles. Therefore, weighting rnateriai such as ground limestone need only be stirred into an oil containing lecithin and'calcium. chloride-whereupon, the. weighting material becomes dispersed :ship ,the: coated material to thewell for mixing into an a 7 .';oil, base-:to.form the drilling ,fluid The ocating need pubtbe uniform since when the coatedsolid is; dispersed suitable for my purposes.

in the oil base, some of the treating materials dissolve in the oil. From the oil solution a coating then is deposited over the previously uncovered portions of the solid particles. Thus, while it is possible to grind the solids with the liquid treating material to obtain a uniform coating of the liquid on the surfaces of the particles, it is satisfactorysimply to stir into the liquid treating'materials sufficient of a dry finely divided solid, such as ground oyster shells, to absorb the liquid and produce a drilling fluid additivesufiiciently dry to be hwdled in paper bags. Since dry calcium chloride and'other salts can be obtained in bags, it may be desirable to handle the salt in this readily available form, only the lecithin or other surface active agent being'deposited on a solid carrier for convenient handling as a dry additive.

When reference is made'to lecithin in this application, commercial lecithin is usually the material indicated. Commercial lecithin generally'consists of only about onethird lecithin, one-third cephalin, another phosphatide, and one-third soybeanoil employed as a solvent.

The term lecithin should not be restricted to this meaning, however, since lecithin in other forms is also When a limitation to commerical lecithin is intended this term will be specifically used. The reaction product of commercial lecithin with aqueous calcium chloride solution appears to form over a wide range of calcium chloride to lecithin ratios. Usually, slightly more calcium chloride'by weight'than commercial lecithin is used since more calcium chloride than lecithin hasbeen' found desirable in drilling" fluids. The reaction product'is norma'llyf produced bysimply stirring together commercial lecithin and a concentrated aqueous calcium chloride solution. The resultantiproduct is aJrhick paste in which free water frequently is by adding a little thin oil, such as No. 2 fuel oil, to the drilling fluids. More fuel oil, for example about 10-percent by volume, may be employed if desired.

In discussing and claiming concenrtates for use inpreparingmy oil'base drilling fluid,-it is convenient to'use the term consisting essentially of calciumchloride and When this term is employed in connection lecithin.

fluids prepared with less viscous oils, on the other hand, can withstand more water contamination before viscosity and gel strengths become excessive. In general, for preparing oil base drill fluids, an oil with a viscosity in the range from about 2 to 200 centipoises should be selected. This includes most crude oils in the United States. If the crude oil'is too thick, it can be cut back with a light oil such-as kerosene .in 'order to meet the initial viscosity requirements. If a fraction of crude petroleum is used as the "oil base, an operable drilling fluid can be prepared even iftheviscosity is as low as one or two centipoises. Solids tend to settle rather readily from "such drilling fluids, however. In addition, if water is prescnL the water disperses into droplets upon mixing, but thesedro'plets also settle rather rapidly leaving a layer of oil on top of the remaining emulsion. The droplets do not appear to coalesce seriously, however, so

a ver'y'liniited amount of stirringiis adequate'tdredistions or petroleum such as fuel oil, diesel oil, lubricating oil, -or'the like.

Most crude petroleum oils 'co'ntain materials such as 'asphaltens andthe like which affect-materially the properties of the final drilling fluid. Therefore, it is frequently possible tofor'tn drilling fluidshaving good properties .with crudeoils' having viscosities somewhat below 10 "centipoises. ,If a crudepetrolcum oil isto be used as the base oilv inpi'epa'ring a commercial batch of drilling fluid, it will begenerally desirable to prepare a small pilot batch jfirst'to determine exactly what thefinal drilling fluid properties WilLbeQ --If the final drillingfluid is top viscous, thezcrude petroleum should bediluted with a non-viscous oil,before preparationof theprincipal batch. If theipilot batch hasinsulficient viscosity orgel strength, the crudepetroleum oil should'be diluted with a viscous "oil,and-.possibly more calcium chloride and lecithin should be added. a

To' avoid fire hazards, it-is usually desirable to observe a'-120- F. m'inimum fia'sh point-limitation in selecting 'an oil base. Most'crudeoils will meet this limitation after with a composition, the term is-intended to indicate=a composition which may contain other ingredients,- but which is free from materials which would destroy the effectiveness of either the calcium chloride-or -lecithin.

, For example, the composition may contain the cephal-in and soybean oil normally associated with lecithin. The composition may also contain absorbent solids used to dry up the liquid product to form a solid concentrate or oil used to thin the product and form a liquid conc'en- Other inert solids and liquids may also be pres- Small quantities of even such'contaminants may bepresent, however, so long as they do not renderineffective a substantial quantity of either the lecithin or calcium chloride or both. I q

The various asp ectsof the drilling fluid willnow be considered in moredetail.

I The oil may consist'of any mineral, vegetablei-or animaloil but the more viscous ones in general produce bettengel strengths-"and lowerfluid losses. *Drilli ng a littleweathering. In-are'a-s-in which the crude oil" will not meet the 'fiash p'oint specification after weathering,

ithe crude eirean be topped tofform' a suitableoil base,

or an oil with desirablecharacteristics can be brought in from other areas.

- *wATBKcoNrE NT 7 The-drillingfluid should contain at least a. .small amount of water. About .Vz-percent byvolume of water should'be present to dissolvelsome of the calciumchlousually convenient to introduce-both the salt and water "into'the=drilling"'fiiiid 'as asaturated solution bfthe salt 'in the 'water. It'is lpossibleyhowever, to add an excess of'finely'powdered solids'alt' tothe oil and'then add just s'fe eirgh" en ma dissolve the desired amountofsalt." It

' enough waterto dissolve'the' salt and this condition frequen't'ly occurs due to'Watericontaminationfrom various is also possiblefor the drillingfluidto'contain more than sources. :Asfpreviously mentionedfthetreated solids have emulsifying properties lwhich:cause the water ,to

be tightly held in a water-in-oiLtype emulsion. .The

water content oft-heemulsionmay in mostcases betas 'vhigh as 30, I percent by volume before the :viscosity and -gel st'rength'exceed"desirable limits of 250 .centipoises-.for

the viscosity, about 5 grams for initialrgel'.strengthzand 20 grams iortheten minute gel strength, all measured. at about 80 F. For drilling fluids with lower viscosities',

that is, about IOO-centipoises, the initial. gel strength may be as-high as about or grams and thelO minute gel may be as high as 30 or 40 grams. If the drilling fluid is to be used in deep hightemperature wells, the gel strengths can be 2 or 3 timesthe-values given since the higher/temperatures decrease the gel strength of the drilling fluid. with thicker- Oi andwith high concentrations of salts other thanlcalcium chloride, the upper limit on 'water contentmay be as low as percent by volume. .By use of -an ,oil'having, a viscosity below about 50 centipoises; it. is-possible toextend thewater contenttoabout-40 percent by volume before theviscosity and gel strength becomeexcessive.

The. distinction between water contaminated oil base drilling fluids on the one hand andemulsion drilling fluids on the other, is an entirely arbitrary'matter. In the drilling fluid literature: it has been customary'by some authorities to. draw the, line atabout 2 or 3 percent water. That is, oil base drilling fluids containing more than about 3 percent water have been defined as emulsion drilling fluids; This is a reasonable, although. arbitrary,

definition. However, it will be observed that my oil-base drilling fluidsv can contain up to about 40 percent by volume of water and still retain good drilling fluid properti'es.- In order to claim conveniently my drilling fluid with water. contents from about up to about 40 percent, itihasj been found necessary to redefine the term sass-meiavailable commercial oil-base drilling: fluids so. long as an oil base havinga viscosity of-at least-about 10 centipoises was used.

SURFACE AGENT The discussion to thispoint has been limitedto lecithin as the surface active agent. I have found that suitable alternates to lecithin are the ester-type non-ionic .oil soluble surface active agents. For some-purposes the ester free ether-type non-ionic oil soluble surfaceactive agents are also satisfactory alternates to lecithing dn general, the esterstype materials "are esters of polyhydric alcohols with organic acids. Theorganicacid portion should contain 'at 'least- 12, and preferably not more than about 20 carbon. atoms per molecule. The polyhydric alcohols should be water soluble and, if they contain oneor more polyoxyalkylene chains such as tetraoxyethylene,- the total oxyethylene groups should not. exceed about 4 in number to avoid excessivewater solubility. Examples of suitable lecithin alternates of theester type are Span ,80, an-anhydrosorbitol monoole'ate aud Pentamull 126,

oil basefdrilling fluid? to'include water. contents much.

hig-her-than normally considered proper. For purposes 7 of; thispinvention, ,theiterm oil base drilling fluid. is

arbitrarily definedas one containing. up to about; 40

' percent-by volume of aneaqueous .phase.

.fsotmsji" The type of solids employed irrmydrilling fluid does not seem to be critical.

materials'such as blown asphalt which seem to act about A possible exception is soft the-same waywhether in the presence of lecithin and calcium chloride or not. Thus, these materials continue to reduce -the fluidloss of oil base drilling fluids preparedwith lecithin and calcium chloride. The principal limitation'on the type ofzsolids is the degreeof fineness to' which they are ground. When the term finely divided solids is-employed, it will be understoodthat a-sin-gle solid or mixture of solids isintended which has been ground-untilat leastabout 90 percent'willpass a numher 325 screen in the US. Standard Sieve Series (Fin Series) #The term solids is not intended to include materials such as salts which are soluble in-the-water or oil present in my drilling fluid. The'term isintendedto include materials' such as bentonite and sodium tallateswhich are merely dispefsible, as well as solids such ground oyster shells, barium sulfate, diatoma'ceous earth the mono ester of oleic acid and. pentaerythritol. The materials are more completely described in my US. Patent 2,661,334. The ester-free, ether-type materials are, in general, ethers of an alcohol or mercaptan containing at least 12 carbon atoms per molecule with a polyglycol (frequently referred to as an oxyethylene chain) or polyglycerol containing not more than 4 glycol orwglycerol units. An example of such materials-isms tarox A-40l, thetetraoxyethylene ether ofnonyl phenol. The ester-free ether-type materials are more completely.

describ'ed;in -U.S.- ;Patent 2,721,174, .Although these al-' ternates are satisfactoryylecithin is somewhat superior to mostof -themin that the fluidloss ofldrillingfluids prepared withiecithin'isiowerand the gel strength is higher thanwhen most of the'alternates are employed- Furthermore, lecithin is less expensive and a smaller-quantity thereof is required. For these-reasons, lecithin'is greatly.

.' preferred as the surface active agent. The ester-ltype sur iface active agents are preferredto the-ester-free ether-.

type since oil-base drilling. fluids prepared with thevlatter type will not maintain more than about I10 percent by volume of water stably dispersed,- larger amounts of water tending to separate from they oil and carry away a part of the calcium chlorideor its alternates. So long as the water content can be maintained below about 10 percentghowever, an oilebase drilling with good properties can be prepared employing, an ether-typelma .terial, such as the Antarox A-401 mentioned'above in a term is intended to include both the ester-type and ester and the like. At least about '5 pounds per barrelof finely dividedsolidsshould bepresentgin my'drilling fluid, and

preferably about 20 p'oundsper. barrel,. to bring the.

viscosity,: gelastrengthhand fluid loss into the desired.

ranges. ,As much as 200 pounds per barrel of coarsely ground hydratable shale has been, added to an oil base drilling fluid prepared according to my inventionwithout? serious elfects eventhough' thisgdr-illing fluid was also contaminated with 30.percent by volume of fresh water.

More than 100 pounds per barrel of weighting materials;

such'as ground, oyster shells or barium sulfate have been added to, my-drilling-fluid without serious effect so long as suificient coating chemicals were provided to' coat the weighting material. In-spite of the absence of the usual suspending agents, these weighting materials remained suspended in my drilling fluid asgwell asthey do in the,

free ether-type of material. The .j'c'lass of :surface active agentssuitablefor use in. preparing drilling fluids containing'more than about 10 percent'water is more specifically defined, to exclude the. ester-freeethei-typema terial s I 'fl r The, concentration of the surface activeiagent should be between about one-half and about ten pounds per barrel, the loweramount being necessary to obtain an appreci i able effect, and the higher limitation being imposed prin cipally by economic considerations. The preferred range. ofconcentration in oil base drilling fluidsflis between. about'2 and4 pounds per. barrel. Foroil bases having, viscosities below about 10 centipoises, ,more solids. and. surface active agents as well as morc'sal-t, ,should be;

limitations should be observed in preparing an oil base drilling fluid competitive with those nowavailahle,i;it

should be noted that a greatly improved workoveridrilling.

7 fluid can be prepared by adding smaller quantities of the surface active agent to the oil base.

SALT

The discussion relating to the types of salts used, to this point has beenlimited to calcium chloride. However, it has been found that other salts are effective asalternates to calcium chloride in preparing oil base drilling fluids with either lecithin or other surface active agents. In general, water solublesalts of alkali and alkaline earth metals are suitable. Examples include sodium or potassium chlorides, nitrates and sulfates, and magnesium or-barium chlorides, nitrates and the like. All these salts appear to react to some degree with lecithin although none of them form as satisfactory a reaction product'as calcium chloride for purposes of forming or treating oil base drilling fluids; Calcium chloride is also superior to its alternates in that drilling fluids preparedwith this salt; withstand contamination by more water, and have lower fluid losses than those prepared with the alternate salts. As noted later, only calcium chloride should be employed in treating presently available oil base drilling fluids.

METHODS OF PREPARATION method, which is particularly preferred if alternates to lecithin and calcium chloride are employed, is to mix a water solution of the salt: into the oil base containing the surface active agent in solution. Solids are then added to this mixture.

If the invention is to be applied to one of the comrnercially available oil' base drilling fluids, the addition of: the calcium chloride-lecithin reaction product is highly convenient. vHowever, it may be desirable to employ either of the constituents alone, calcium chloride being effective for reducing fluid loss, and; lecithin being effective for reducing viscosity.- A combination of lecithin and calcium chloride is necessary for giving protection.

againstwater and shale contamination.

TREATING PRESENT DRILLING FLUKDS Considering in more detail the application of the inventionto treating of commercial oil base drilling fluids, as previously mentioned, the treatment is particularly applicable to oilbase drilling fluids containing hydrophilic solids. This termshould be considered sufliciently broad to include materials which react chemically with water, for example, quicklime; materials which are highly dispersible in water, for example, sodium soaps of fatty acids; and materials which are swellable by water, for

example, bentonite. A possible theory of the action of my treatment is that it produces a coating of calcium chlorideandlecithin on the finely divided solid particles present in anyoil base drillingfluid, so that a commercial drilling fluid treated with calcium chloride and lecithin actually-becomes almostidentical to one prepared by adding'simplyz-the lecithin and calcium chloride, together with an inexpensive finely divided solid, to an oil base. As-notedinExampleIV, however, saltsother than calcium chloride do not afford a resistance to water contamination equivalent to that provided by the calcium chloride even in simple systems involving only oil, ground oyster shells, the salt and lecithin. The oil base drilling fluidsnow commercially available are rather complex mixtures in which it has been found that calcium chloride is unique inits ability to provide good resistance to water contamination in all of them. Some other salts are fairly effective in some cases, but calcium chloride is efiective in all cases. As previously noted, the ester free ether-type oil soluble non-ionic surface active agents give stability to only a limited amount of water. Therefore, in treating presently available oil-base drilling fluids, the materials should be limited to calcium chloride as the salt, and to oil soluble nonionic esters of polyhydric alcohols and acids having'at least about 12 carbon atoms per molecule as the surface active agent.

Any amount of calcium chloride added to present commercial oilbase drilling fluids helps to reduce the fluid loss and affords some protection towater contamination. However, a minimum of at least 2 pounds per barrel should be added to commercial oil base drilling fluids to. obtain good fluid loss reduction and fair stability to Water contamination. It has been found that more than 3 or 4 pounds per barrel of calcium chloride produces little additional effect and up to 10 pounds per barrel has been found to be relatively harmless except possibly for the rather high viscosity which results. The concentration of surface active agent to be employed in treating commercial oil base drilling fluids can be as low as a trace and" still produce some beneficial effects. However, for good stability to water and shale, and for appreciable viscosity reduction, atleast about 1 pound, and preferably about 3 or 4 pounds of surface active agent, preferablyi commercial lecithin, per'barrel'of drilling fluid should be added. As much as 10 pounds per barrel of commercialilecithin has been used without harmful effects.

Accordingly, the upper limit on concentration of'surfaceactive agent apparentlyis principally economic in nature.

My invention will be more clearly understood by reference to the following examples. In all the data prmented in theseexamples, fluid loss and viscosity were determined, at F. by the methods described in API Code No. 29 Second Edition, July 1942 (tentative). Fluid loss is in: units of cc. of filtrate in 30 minutes. Viscosity isin units. of centipoises. ,Gel strengths were measured by means of a Stormer viscosimeter and are given in terms of the. number of grams which were required to cause theviscosimeter cup to start to turn immediately after stirring; (initial) or after the drilling fluid had remained'quiescent for 10 minutes ('10 minute gel strength). Where. the

amount of Water contamination is stated, the figure is in;

Example I A series of drilling fluids Was prepared containing various concentrationsof commercial lecithin andcalcium chloride. The-oil base in every case was a West Texas crude oil from the Slaughter Field having a viscosity of 8 centipoises at 80 F. and a gravity of 32 API. The solid added was 20 pounds of ground oyster shells per barrel of uncontaminated drilling fluid, this limestone'be ing ground so that at least percent passed a 325' mesh screen. The calcium chloride was added in the form of a saturated solution, containing about 40 percent by weight calcium chloride. The concentration of the salt is presented in terms of percent by volume of the saturated salt solution, based on the oil, and also in termsof pounds of anhydrous calcium chloride per barrel .of'uncontaminated drilling fluid.

. v TABLE I 0501 GelStr., Grams Fluid Loss Oommer- Water a1 Oon- Viscosity, Percent Lecithin, tam, cpse. 10

325d. #lbbl. #lbbl. Percent Initial min. 80 F. 190 F.

4 None 43 1 7 3 4 None 40 0 1 r 6 4 None 50 1 4 20 4 None 70 1 7 60 4 None 135 1 10 so 4 one 23g 2g 3% 0X16 N 2? i v V 0116 None 50 1 4 6 4 s 54 1 4 4 20 110 1 i e -4 N 2 0118 i N i '3'? 0118 0116 2{ N a 2 it 0119 1 4 N 40 1: g i 0118 V 40 170 s 13 1.0

* lt will be noted =from the above table that as little "as LS'percent-Samrated calcium chloride solutiomand =0i5 pound per'barrel of commercial lecithin produces a very satisfactory drilling fluid. 'These'lower ,values -were se1ected-as the lowest which could belaccurately andconveniently handled in the laboratory. It isiapypa'rent that smaller quantitiescould be used in field operations. The most desirable concentrationsseeni to be percent saturated cailc'iu' {in '4 6 ds ofcofiimercial Example 11 To determine. the effect of using various oil bases, a series of drilling fluids was prepared using various oils. In all cases the treating chemicals were 3 percent by volume, of a saturated aqueous solution of calciumchloride and 4 pounds of "commercial lecithin per barrel of .drilling fluid; Each drilling fluid contained 20 pounds per'barrel of ground oyster shells prepared-as described in Example I." The resultsare presented in TableIL' TABLE 11 V Gel Stu, Grains I .911 Base; w Added Fluid Loss: 1 N a water, -Vis., V a Percent epse. Field Area Vise, Gram, By Yol. Initial min; 80 F. 190 F.

a p cpse. -API Little Bufialo Basin-.. W3;i)mgdS15%fuel 160 19 8 None 180 1 1 5.5 7.0

. o a e Do dn' 160 19.8 40 250+ 3 8 0.5 Sour Lake .Texas 51 26.5 None 56 0 1 0.0 1 D0 .51 26.5 40 105 1 1 0.0 Sholem Alechem 22 r 29.5 None 98 1 2 5.0 Spindletop 31. 1 None 31 0 0 3. 0 Do 15 31.1 40 80 0 1 3.5 Slaughter"... 8 32.0 None 50 1 4 4. 0 Do 8 j 32.0 150 1' 6 0.5 Fuel Oil 1' 33. 2 None 6 0 0 11. 6 .Do 1 33.2 7 40 13 0 0 10.0 Light Lubricating Oil 75 62 250+ 15 20 3. 8 Do l 52 72 1 1 32.0 D0 7 52 V 225 '15 20 3.4

Do 59 1 1 Do 45 190 12 14 3.9

drilling fluid; obviously withstood treatment by up 16 pounds, per barrel ofcalciumfchloride and at least 10 pounds o f tcommerciali leeithinper barrelwithout difficulty.

- .;Stability to*at least 4(ltperc ejnfft water contamination is; well shown. Iti;v'vill beappa-riitthat 'by limiting 111183;

' In the a bove table it will be ob served that all oils tested amount of calcium'chloride to eabout 10 or 20 pounds 1' contaminated by water. Even drilling fiuidscontaminated withwater, however, do not have high fluid lossrates at elevatedtemperatures. j 7

produced satisfactory drilling fluids. All these drilling fluids, with one exception, also'withstood contamination by water amounting to 40 percent by volume of the original drilling fluid. The exception 'is' the drilling fluidusing Little Buifalo Basin crude oil as abase.

When a little more fuel oil was added to this contaminated drilling fluid to reduce the viscosity of "the oil phase, the viscosity of the emulsion'dropped down into an operable range below 250 centipoises. The stability to high tem- V perature should also be noted; The drilling fluid prepared 'with fuel oil, while operable, permitted solids to settle to suchan extent that frequent mixing was required. When water was added, the water dispersed into droplets, but these droplets settled, permitting a layer of oil to collect on top. The water droplets did'. not, however, tend to coalesce seriously, so a little mixing redistributed them-throughout the oil phase. It will be noted that than calcium chloride.

11 the more viscous light lubricating oil fractions with viscosities of 40 or 50 centipoises produced oil base drilling fluids with fluid losses which were rather high but still operable for many purposes. These drilling fluids could be diluted with 62 percent added water (38 percent of the total final volume) and still retain good properties. The gel strengths were a little high, but as previously noted, this is sometimes desirable for deep high temperature wells.

Example Ill TABLE III Added Gel Strength, Fluid Water, Visc., grams Loss, Surface Active Agent Percent cpse. cc.l30

By Vol. min. at

Initial 10 min. 80.-F.

1 8.0 cc. of water separated from this filtrate.

Span 80 is anhydrosorbitol monooleate, Pentamull126 is the'mono ester of oleicacid and pentaer-ythr'itol and Antarox A401 is the tetraoxyethylene ether of nonyl phenol.

Oil base drilling fluids prepared with oil-soluble nonionic surface-active agents other than lecithin obviously agent was 4 pounds'per barrel of commercial lecithin and the'solids consisted of 20 pounds per barrel of -ground oyster shells prepared as described in Example'l. The properties of the drilling fluids are shown in Table IV. Properties of a. drilling fluid employing calcium chloride as the salt are presented for comparison.

TABLE IV Added Gel Strength, i Fluid-Less Water, grams W Salt Per- Vlsc.,

cent cpse. By Vol. Initial 10 80 190 Calcium Chloride. 5O 1 4 4.0 6. 5 Do 150 1 6 0.5 3.6 42 1 4 "[5 13.0 170 10 20 2.0 34 1 2 11.5 16.15 170 9 29 L5 According to these data, drilling fluids preparedwith alternates to calcium chloride have operable characteristics, the only property in which improvement is desirable being a rather high fluid loss compared to the drilling fluid prepared with calcium chloride. The data-show that:calcium chloride is considerably superior not only in reducing-fluid loss, but also in stabilizing the drilling. fluid against water contamination. It will benoted that all the salts produce drillingfluids which arehighly stable to heat. Y

Example V Several drilling fluids were prepared with .a number of'solids in various concentrations. In all thesetesta', commercial lecithin was employed as the surface-active agent and calcium chloride as the salt. The oil base was the .West Texas crude oildescribedinExample I except drilling .fluids 16, 17, and '18 in which a crude oil from Sour Lake, Texas, was used as the. oil base. The com- ;positions and properties of these drilling fluids are indicated in Table V.

TABLE V 5 n I 09.01, Added Gel Stn, Grams Fluid Loss, Lecithin, Sol'n, Water, Vise, cc./30 min #lbbl. percent percent cpse. at 80 Material 1 #lbbl. by Vol. by Vol. Initial 10 min.

2 1.5 None 150 2 1.6 None 28 2 1.6 None 33 0 1 5.5 2 1.5 142 3 6 1.5 4 None None 28 0 0 140 Oyster Shells 4 None None 43 1 7 as Aqimqol 4 3. 0 None 48 1 4 7. 0 Oyster Shells 20 4 3- 0 None 54 1 4 4. 0 do 20 4 3.0 40 150 1 6 0.5 Oyster Shells and Shale cuttings.-. 3g 4. 3.0 40 130 a 12 1.0 u (in v 53 4 3.0 40 130 a 11 5.0

.Oyster Shells and Blown Asphalt..- 4 NOfiB 4 1 2 Oyster Shells 20 4 6.0 None 71 1' '3 4.5 Drilling Fluid 13+110 bSJbbL'Barmm Sulfate 93 1 .1 1 Drilling Fluid 14+2% fresh water 112 l 1 2. 0 Oyster Shells 4 6-0 I ne 1. 1 0.0 Drilling Fluid 16+110 bsJbblxBarium Sulfate I 57 1 l "0.0 Drilling Fluid 17 heated to 300? .F. at 4,000 p.s.1.g. pressure or 15 hours, 51 1 1 0.0

cooled and stirred have quite'satisfactory characteristics, the lecithin preparations being somewhat superior in gel strength and fluid loss,'and the ester-containing types being'more stable to water contamination.

The ground shale in the second drilling fluid was=a-hydratable shale, from the Texas Gulf of Mexico coastal area, ground until percent passed a 325 mesh screen. The shale cuttings listed later were the same material much more coarsely ground to pass a 20mesh screenso they would simulate fine bit cuttings occurring in 'drilling operations. The oyster shells were'the same=as described-in Example I. Aquagel is a finely divided bentonite, of which percent passes a 325*mesh screen and is obtainable from the Baroid 'Sales Division of 'the in Table VI.

, National Lead Company. The barium sulfate was ground to the same fineness as the "Aquagel. A comparison of the fluid lossaobtained by useiof shale ground until 90 percent passed a 325 mesh screen and oystershells' or bentonite ground until 95 percent I of water. Drilling fluid number 12 was prepared to determine if blown asphalt would function as a fluid-loss reducer in the presence of the solid-coating materials of my invention. The data indicated that the blown asphalt continues to be efiective. A comparison of drilling fluids 13 to 14 and of 16 to 17 demonstrate the ability of the drilling fluid to suspend weighting materials without adverse eflects on its properties. Settling rates of the weighting materials were comparable to rates typical of present commercial oil base drilling fluids. The properties of drilling fluid 15 shows the ability of a little water to reduce the fluid loss of the weighted preparation. Finally, the properties of drilling fluid '18 demonstrate the stability 7 of the drilling fluid at sustained high temperatures and pressures.

Example VI Five commercial oil-base drilling fluids were prepared having approximately the following compositions, all

" parts being by weight unless otherwise indicated:

200 parts of a 22.8 gravity Sholem- Alechem crude.

, 120 parts of a bentonite wet with Sterox CD, a-nonionic, fwater-soluble, surface .active agent prepared by reacting about 10 moles of ethylenejoxide with one mole of abietic acid or tall oil.

190 parts of ground limestone. V r V v This composition was prepared according to copending application Ser. No. 144,856,- Lummus et a1. B. 240 parts of stove oil.

60 parts of ground limestone. 30 parts of blown asphalt.

20 parts of quicklime. parts of water. This composition was prepared according to U.S.

Patent 2,356,776, Miller. C. 200 parts of diesel oil.

50 parts of blown asphalt. parts of sodium silicate. 10 parts of tall oil. 5 parts of water. This composition was prepared according to U.S. Patent 2,350,154, Dawson et al. D. 1000 parts of 28 gravity crude oil from Velma Field in Oklahoma. 135 parts of a concentrate made up of 50 parts stove oil. a 50 parts potassium resinate. 5 parts hydrated lime. '10 parts water. 5 parts ethylene glycol. '15 parts bentonite. This composition was prepared according to U.S.

Patent 2,573,960, Fischer. E. Same as A except using the West Texascrude oil described in Example I as the oil base.

Properties of these drilling fluids with and without treatment with calcium chloride and lecithin, and with and without 40 percent water contamination are presented of commercial lecithin per barrel, and 1.5 percent of a saturated aqueous solution of calcium chloride. Water TABLE VI Y 2' 40% 1 Gel Stren th; Fluid-Loss Drilling Treated Water Vise, Fluid Added c'pse. Y v

- E Initial 10min. 80 F. 190 'F.

" $5 3+ i '3 3'8' A 180*. '1 I we 0.0 1.2

160 1 7 0.0 .23. 1t t8 0 66 o 2 0.5 1.0

250 0 3 0.0 60 O 0 19.0 E No Yes... 250+ 3 16 Yes No 120. 2 5 1.0

Yes---" Yes..- 178 2 5 The surprisingly complete stabilization to water contamination of the hydrophilic solids in all the above drilling fluids is to be noted. The viscosities remained within operable limits, and the gel strengths were almost entirely unaffected by the presence of water. The reduction of fluid loss at high temperature is probably due to the plastering effects of the solids coated with calcium chloride and lecithin. g

It will be apparent from the above discussion and examples that I have provided a'low cost oil base drilling fluid in which weighting material 'or other solids can be easily dispersed in the oil base to ialford'satisfactory plastering and gel strength properties. The drilling fluid In every. case the treatment was 2 pounds of the oil.

withstands'contamination by large quantities of water and shale. The fluid loss varies little with changes in temperature. The density of thedrilling fluid can be easily increased by adding a finely divided weighting. 'material which readily disperses in my fluid.

The invention has been shownztobe applicable also to the j" treatment'of existing oil base drilling fluids to stabilize these drilling fluids against the effects of high tempera tures' and of water and shale contamination.

Although several specific theories andv examples are" presented, it will be apparent to those skilled in the drillingfluid art,'that many additional variations fall within the scope of my invention. Therefore, it is my intention to be limited not by thme examples and theories but rather by the following claims.

I claim:

1. A composition for use in preparing or treating oilbase drilling fluids consisting essentially of calcium chloride and lecithin in which the ratio of calcium chloride to lecithin is in the range of 0.2/1 to 20/ 1.

2. The composition of claim 1 in which said lecithin is commercial lecithin. g

1 3. The composition of claim 1 which includes in addi tion to the calcium chloride and lecithin suflicient finely divided solids to form a dry free-flowing powdery composition. 7

4. The composition of claim3 in which said lecithin is commercial lecithin.

'5. An oil base drillingfluidcomprisingianoil having a viscosity below about 200 'centipo ises, lecithin in a com centration between about' /z and about 10 pounds per barrel of drilling fluid, calcium chloride in a' concentra- 7 1'5 7. In the process ofservicing a well the step of circulating in said well the drilling fluid defined by claimS.

8. "In'the process-of servicing .a --well the step of circulating in said well the 'drillingfluiddefine'd by claim-16.

9. An-improved o'il' base drilling fluid comprising an initial oil base drilling fluid containing; a'fi'nely divided "solid; water in an amount between about-V2 and about 40 percent by volume of said improved oilbase'drilling flui'd; calcium'chloride inan amountlbetweenqabout 2 improvedroil: basetdrill-ing fluid. 7

References Cited in the file of this patent :and' about 10 pounds per barrel of saidimproved' oil base 10 2;772,073

UNITED STATES PATENTS Dawson May 30,1944 Menaul Sept. 14, 1954 "Fischer Mar. 20, 1956 Johnson ,Nov. 27, 1956 

5. AN OIL BASE DRILLING FLUID COMPRISING AN OIL HAVING A VISCOSITY BELOW ABOUT 200 CENTIPOISES, LECITHIN IN A CONCENTRATION BETWEEN ABOUT 1/2 AND ABOUT 10 POUNDS PER BARREL OF DRILLING FLUID, CALCIUM CHLORIDE IN A CONCENTRATION BETWEEN ABOUT 1/2 AND ABOUT 80 POUNDS PER BARREL OF DRILLING FLUID, WATER IN AN AMOUNT BETWEEN ABOUT 1/2 AND ABOUT 40 PERCENT BY VOLUME OF SAID DRILLING FLUID, AND INSUFFICIENT TO PRODUCE A DRILLING FLUID VISCOSITY EXCEEDING 250 CENTIPOISES, AND A FINELY DIVIDED SOLID IN A CONCENTRATION OF AT LEAST ABOUT 5 POUNDS PER BARREL OF DRILLING FLUID. 